How you are alerted to change the filter depends on how the control was configures at start-up. there are 2 types of filter, media (which is the solid filter thats been around forever) and EAC - electronic air cleaner (which works just like the electronic air cleaners you see in stores that have no filter). When the control is programed for use with a media type like the 4 inch filter you have the control will alert you when to change based on static pressure...for exaple you mentioned that your static pressure was at .45, the infinity system remembers that reading and will indicate the filter is 100% used around .76-.80 static. With an EAC the static pressure does not change so the control initiates a timer to tell you when to clean the filter.